1. Field of the Invention
This invention relates to an optical memory device, and more particularly to an optical memory device comprising a recording layer made of the material having a photochromic property, and performing recording and reproduction of information by use of light such as laser beam.
2. Description of the Related Art
In recent years, an optical memory device that can record, reproduce and erase information by use of light is an increasing need as a memory device of high density and high capacity. Among the conventional optical memory devices, an optical memory device using a photochromic material for an optical memory layer (a recording layer) has been well known. Particularly known structure of the optical memory device is as shown in FIG. 2 which comprises a substrate 11 and a series of optical memory layers R.sub.1, R.sub.2 . . . R.sub.n formed in this order over the substrate 11, the optical memory layers each being made of a photochromic material and being capable of recording information by use of light of specific wavelengths .lambda..sub.1, .lambda..sub.2, . . . .lambda..sub.n, respectively, so that the light application of specific wavelengths to respective optical layers provides a multi-recording with n layers (Japanese Unexamined Patent Publication SH062-165751 (1987)).
Upon recording information, a laser beam of high energy is applied to the optical memory layers, whereby information is written in the optical memory layers through a chemical change of the structure of photochromic material. Upon reproduction, the information recorded is read out based on the intensity of transmitting light of a laser beam of low energy applied to the optical memory layers.
The conventional optical memory device does however have such a problem that when laser beam is applied to an i-th layer (i.ltoreq.n) of the optical memory layers to record information, the temperature of the i-th layer rises with temperature of adjacent layers [(i-1)-th and (i+1)-th layers] also rising, resulting in that record of information in the (i-1)-th or (i+1)-th layer vanishes or the optical memory layer (the i-th layer) itself may be deteriorated.
The invention has been accomplished to overcome the above problem. An object of the invention is to provide an optical memory device which is less in temperature rise by the irradiation with light upon recording of information, thereby causing no vanish of recorded information and no deterioration of the optical memory layer.